With excellent characteristics including injection moldability and mechanical properties, polyester and polyamide resins have been used in a wide range of fields such as mechanical machine parts, electric/electronic components, and automotive parts. Being crystalline plastics with high melting points, polyester and polyamide resins require melt-kneading type extruders and injection molding machines with a high operating temperature.
Being essentially combustible, most polyester and polyamide resins should be modified to have features against fire, i.e. flame retardancy, in good balance with other common chemical and physical characteristics when used as material for mechanical machine parts, electric/electronic components, and automotive parts. In many cases, they have a high degree of flame retardancy to meet the V-0 requirements specified in UL 94.
As a means of making polyester and polyamide resins flame-retardant, a halogen-based organic compound and an antimony compound are generally added to the resin as flame retarder and flame retardation assistant, respectively. However, increasing numbers of environment-conscious people are worrying about the influence of halogen-based organic compounds on environment.
In recent years, there has been stronger call for the use of non-halogen type flame retarders completely free from halogens, and it has been proposed to add an appropriate phosphinic acid salt as flame retardant to a thermoplastic resin.
Patent documents 1 and 2, for instance, have disclosed the addition of a phosphinic acid salt and a nitrogen-containing compound, as non-halogen type flame retarders. However, if such a phosphinic acid salt is used as flame retarder to make polyester and polyamide resins flame-retardant, the flame retarder can generate a corrosive gas, which then acts to corrode the screws of kneading machines or the molds of injection molding machines.
It seems also likely that metal parts such as terminals that come in contact with molded articles produced from the resulting flame-retardant thermoplastic resin can be corroded to cause contact contamination.
Thus, the above problem cannot be solved by the techniques proposed in Patent documents 1 or 2, and development of effective solutions has been an essential issue. Accordingly, new techniques that can solve the above problem and meet present requirements in the fields of mechanical machine parts, electric/electronic components, and automotive parts have been strongly called for.